Electrical velocimetry for measuring cardiac output in children with congenital heart disease  K. Norozi, C. Beck, W.A. Osthaus, I. Wille, A. Wessel, H. Bertram  British Journal of Anaesthesia  Volume 100, Issue 1, Pages 88-94 (January 2008) DOI: 10.1093/bja/aem320 Copyright © 2008 British Journal of Anaesthesia Terms and Conditions

Fig 1 Surface ECG, impedance waveform [−dZ(t), also known as ΔZ(t)], and the electronically differentiated first time-derivative of −dZ(t), −dZ(t)/dt, obtained from a 25-day-old male (HR=142 beats min−1, SV=3.3 ml, CO=0.47 litre min−1). Note that the impedance change −dZ(t) and its rate of change, −dZ(t)/dt are given in their inverted form, which is the traditional presentation because the shape of the −dZ(t) waveform exhibits some adherence to an aortic pressure tracing. The marker labelled ‘Q’ on the ECG marks the beginning of ventricular depolarization and thus the onset of electro-mechanical systole. Shortly after aortic valve opening, which is indicated by the marker labelled ‘B’, the −dZ(t) waveform exhibits a significant upslope and, consequently, its time-derivative −dZ(t)/dt, a nadir which is indicated by the marker labelled ‘C’. The amplitude at the point which in the traditional presentation is depicted as a positive deflection is the maximum slope or peak rate of change of the transthoracic electrical impedance during a particular cardiac cycle, and measured beat-to-beat. The time-to-peak (rise time) of −dZ(t)/dt is concordant with the time to peak of −dv(t)/dt of the aortic blood velocity waveform. The magnitude at the peak of −dZ(t)/dt, that is |(dZ(t)/dt)MIN|, is analogous to the magnitude |dv(t)/dt)MIN| of this waveform. The first-time derivative of the impedance waveform, −dZ(t)/dt, exhibits a deflection at the time of aortic valve closure, which is indicated by the label ‘X’. The temporal interval between points B and X is defined as the left ventricular ejection time. British Journal of Anaesthesia 2008 100, 88-94DOI: (10.1093/bja/aem320) Copyright © 2008 British Journal of Anaesthesia Terms and Conditions

Fig 2 Scatter-plot of the data from 32 invasive measures of COF and corresponding COEV measurements. British Journal of Anaesthesia 2008 100, 88-94DOI: (10.1093/bja/aem320) Copyright © 2008 British Journal of Anaesthesia Terms and Conditions

Fig 3 Bland and Altman analysis of cardiac output measured by electrical velocimetry (COEV) and that determined by the direct Fick-oxygen (COF) in 32 infants and children. Note: The cardiac output is not indexed but given in absolute values. The bias between COEV and COF was 0.01 litre min−1. The upper and lower limits of agreement (±2 sd) were 0.47 and 0.45 litre min−1, respectively. British Journal of Anaesthesia 2008 100, 88-94DOI: (10.1093/bja/aem320) Copyright © 2008 British Journal of Anaesthesia Terms and Conditions